OBJECTIVETo investigate the effect of gradually induced disordered occlusion (GIDO) on the expression of tumor necrosis factor-alpha (TNF-alpha) in condylar cartilage in rat.

METHODSFourty-eight SD rats, aged 8 weeks, were included, and were divided into experimental and control groups randomly, with the same gender distribution. By inserting elastic rubber band the first mandibular lower and maxillary upper molar was moved medially. Four weeks later the third mandibular lower and maxillary upper molars were moved distally with the same method. In this way the GIDO was established in rats. The rats were sacrificed at the end of 2nd, 4th, 6th, 8th week respectively after the application of the GIDO and the temporomandibular joints were stained with HE. The cartilage thickness was measured. The expression of TNF-alpha in condylar cartilage was examined by immunohistochemistry and calculated by the percentage of positive cells areas.

RESULTSThe cartilage thickness increased in 4th, 6th, 8th week subgroups of experimental group (P < 0.05). Typical degenerative changes were observed in the experimental group. The expression of TNF-alpha was mainly in the hypertrophic layer of the condylar cartilage. Compared with the age-matched control group, the expression of TNF-alpha in experimental group increased at the end of 2nd, 6th and 8th week (P < 0.05), but kept the same level at the end of 4th week (P > 0.05).

CONCLUSIONThe present results suggest that TNF-alpha take part in the procedure of the abnormal remodeling activities of condylar cartilage in GIDO rat model. The catabolism in condylar cartilage in GIDO rats was even obvious when the experimental period was longer with more serious GIDO.